1. Field of the Invention
The invention relates to the mechanical arts. In particular, it relates to a mold for forming a container with an opening, from a deformable material.
2. Description of Related Art
Molded plastic containers, more specifically, containers molded from expanded organic polymer material, are available in numerous shapes as packaging material for a variety of articles, such as eggs, take-out foods, light bulbs, seedlings and the like. The containers are particularly useful to protect the articles against impact, temperature changes and other adverse environmental effects. A large proportion of the containers are provided with closures which must withstand rough and rapid handling, or repeated opening and closing. A simple and effective closure is obtained by providing a latch, extending outwardly from or adjacent to one edge of one half of the container, which is insertable into a latch opening provided in the other half. The latch can be in the form of a flat tab or round protuberance, or the like. The latch can be provided in the bottom of the container and the latch opening provided in the lid, or vice versa.
U.S. Pat. No. 3,845,187 describes a continuous method for forming a container with an opening from a sheet of plastic. The opening is formed during the molding operation by obliquely and resiliently pressing a hole former through the plastic, until it contacts a die surface. Use of a spring or other resilient member to spring-load the hole former or the oblique surface serves to "tighten up" loose tolerances. However, limitations to this method arising from the design of the mold components and from the range of utility of the apparatus. The requirement that the hole former be in contact with the die surface, when it cuts through the plastic sheet, necessitates sharpening or replacement of its dulled or blunted cutting edge.
U.S. Pat. No. 4,108,941 describes a continuous method for forming a molded plastic container having an opening, where the opening is formed by the vertical shearing of a sheet during the closure of the mold parts. Shearing is accomplished by the movement of an upper key past a vertically aligned lower key, at a distance which is less than the thickness of the sheet, during compression of the mold parts.
U.S. Pat. No. 4,446,088 describes a mold for producing openings in thermoplastic cartons by the relative movement between a male key and a female key having flat surfaces transverse to the closing motion of the mold. The flat surfaces are biased into engagement with one another. To promote registration of the keys, as the mold closes, the female cutting edge engages a beveled edge on the male key against the bias in a motion transverse to the closing motion.
The mold in accordance with the present invention is an improvement upon the molds described in U.S. Pat. Nos. 3,845,187, 4,108,941 and 4,446,088, which patents are incorporated herein by reference. It has been discovered that, when in accordance with the invention, the mold incorporates a key which is pivotable along a plane normal to the direction of the closure of the mold parts, the alignment of the upper and lower keys is greatly facilitated. Moreover, once aligned, the keys stay aligned for longer periods of time than is possible with conventional molds. This increases the accuracy of the formation of the latch opening and reduces the frequency required for sharpening or replacing the keys.
The adjustable design of keys in accordance with this invention permits the mold to be used without spring-loading the components. However, particularly with very loose mold components, the components can be spring-loaded.